A trigger notification should have gone out, but did not – additional considerations
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Issue Symptoms

A ticket was updated and a trigger didn't send a notification even though the ticket seemingly met the criteria of the trigger.

Conditions

The user who would normally receive the email notification from Zendesk Support was included as a CC or To on the original inbound email.

Resolution

To prevent the scenario where a user receives multiple emails for the same update, if they are a recipient of the email most recently updating the ticket, any trigger notification that is supposed to be sent for that update is suppressed.

This is because the user would have already received the message in their inbox from the most recent email (even if they sent the update themselves).

If you would like to confirm this occurred on the ticket in question, you can use the API to confirm your suspicion. Just access https://{your subdomain}.zendesk.com/api/v2/tickets/{ticket number}/audits.json

You will want to look for something like this coinciding that that ticket update: